Motor Unit and Electromyogram (EMG ) s4

Motor Uunit and Electromyogram (EMG)

Motor unit :

A single motoneuron and it’s axons suppliesy not only just a single muscle fiber, but also manyseveral muscle fibers through its axon. AThe muscle fiber that is supplied by one motor neuron through its single axon andalong with its branches are is called a Mmotor Uunit. The numbers of muscle fibers in a motor unit varies. It is has been observed in cat leg muscles that approximately 120, –165 fibers are present in one motor unit.

Electromyogram (EMG)

A mMotor unit activity is measured through placing recorded by inserting a coaxial electrode in to the muscle that is to be studied. Then, the electrodesthey are connected to the electromyography. A recording is obtained during muscular activity . This recording is called an electromyogram (EMG).

A hypodermic needle can be madeconverted in to a coaxial electrode by introducing an insolatedinsulated inner wire with in it. Potential differences is are recorded from a small volume of the muscles in the immediate neighbuorhood of the tip of the needle tip. Thus, it is has been observed that most of the electrical activity is from the active fibers near the electrodes . Sometimes, surface electrodes is are used in stead of coaxial deep muscle electrodes. In this recording method, two surface electrodes are placed on the skin overlying the muscle to be studied over the to be studied muscle’s at a reasonable distance from each other.

When the muscle is at rest, there is no action potential is recorded but ; however, as soon as the muscle becomes active, potentials are recorded. The potential recorded during Aactivity is attributed as a result of to the asynchronous discharge of motor units in the vicinity of the electrodes. During minimal voluntary activity, only a few the number of motor units discharged is lesss, and as the voluntary effort increases, the more number of units is activated is more. This is called known as recruitment of motor units recruitment.

Gradation of muscular activity is a part of the function of a number of motor units activated. Electromyographic studies have clinically importance in diagnosizs of motor unit disorders including peripheral nerve injuries, and neuromuscular disorders such as myotonia and myasthenia gravis, so on and so forth.

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